Secondary batteries called lithium ion batteries, currently attracting attention. They can broadly be classified into two categories of so called lithium ion secondary batteries and lithium metal secondary batteries. The lithium metal secondary batteries utilize precipitation and dissolution of lithium for the operation. Besides, the lithium ion secondary batteries utilize storage and release of lithium in the charge-discharge reaction. These batteries both can provide charge-discharge at large energy densities as compared with lead batteries or nickel-cadmium batteries. By making use of this characteristic, in recent years, these batteries have been widely applied to portable electronic equipment, such as camera-integrated VTR's (video tape recorders), mobile telephones, and notebook computers. In accordance with a further expansion of applications, the development of lightweight lithium ion secondary batteries such as to allow high energy densities has been advanced, as a power source of the portable electronic equipment. Further in recent years, durability, long service life, and safety are also strongly required, with the inclusion of a power source of the automobiles.
Regarding a liquid electrolyte, a particular combination of materials has widely been employed, for lithium ion secondary batteries or lithium metal secondary batteries (hereinafter, these may be collectively referred to simply as a lithium secondary battery), in order to realize high electric conductivity and potential stability. That is, a carbonic acid ester-based solvent, such as propylene carbonate or diethyl carbonate, is employed, in combination with an electrolyte salt, such as lithium hexafluorophosphate.
On the other hand, with respect to the composition of a liquid electrolyte, a technique for making various kinds of additives to be contained in a liquid electrolyte is proposed, for the purpose of improving cycling characteristics and the like. For example, in Patent Literature 1, improvement in the battery performance has been tested, by addition of ethyl cyanoacrylate.